It is well known in that field to use power amplifiers in various radio circuits or cards so as to amplify the radiofrequency (RF) signals, which are initially signals with a low amplitude and power, before transmitting them to a radio antenna.
Power amplifiers are traditionally subject to several forms of protection, so as to avoid damaging the components, in particular the transistors, in case of operation outside the reliability ranges set out upon design. Thus, traditionally, a power amplifier is protected in terms of temperature and current. These forms of action are achieved using corresponding sensors and act directly on the power supply of the power amplifier to be protected, by cutting or decreasing the power supply voltage.
Furthermore, a high standing wave rate (SWR), which occurs when the charge of the antenna is very different from the nominal output charge of the power amplifier, may cause damage to the transistor(s) of the power amplifier.
This known problem is traditionally resolved by using a directional coupler 12 making it possible to measure the amplitude of the direct or incident voltage Pi and the amplitude of the reflected voltage PR reflected toward the amplifier, as illustrated in FIG. 1. The outputs of the coupler 12 are transmitted to a processing circuit 14 that applies an attenuation value VATT to the power supply voltage of the power amplifier 10.
However, the bulk of the couplers is not negligible, and sometimes makes them difficult to integrate into very compact products. In particular, in the field of high-frequency (HF) and very high frequency (VHF) bands, the production of power couplers requires the use of transformers wound on ferrite cores, which are expensive to manufacture.
Furthermore, in particular in the field of mobile telephony, SWR protection solutions implementing a protection circuit dedicated to each transistor of a power amplifier have been developed. This type of solution by specific circuitry also has drawbacks, on the one hand in terms of high design and production costs (which are unacceptable for mid-series), and on the other hand in terms of bulk.
It is desirable to resolve at least one of the drawbacks of the state of the art, by proposing protection for an electronic circuit, in particular for a power amplifier, that is relatively compact and less expensive than the known solutions.